1. Field of the Invention
The present invention relates to variable optical attenuators, and particularly to a variable optical attenuator which can precisely control the amount of optical attenuation.
2. Description of Prior Art
Attenuators are widely used in optical transmission systems for reducing high power transmission signals to acceptable signals for application in a variety of optical apparatuses.
FIG. 1 shows a variable optical attenuator as disclosed in U.S. Pat. No. 4,989,938. The variable optical attenuator 100 comprises a housing 150 containing a first optical fiber connector 140, a first optical lens 160, a first connecting optical fiber 180, a second optical lens 200 separated from the first optical lens 160 by an optical coupling space, a second optical fiber connector 220, a second connecting optical fiber 240, an optical filter 260 and a reciprocating means 280. The optical filter 260 is a flexible film having an optical density gradient which varies along a length of the filter 260. The filter 260 is preferably mounted substantially orthogonally to an optical axis of the optical coupling space.
When the filter 260 is moved vertically, a part of the filter 260 having a different optical density is put in a path of light passing through the optical coupling space. The filter 260 can thus control transmission and absorption of differing amounts of light. By varying the vertical position of the filter 260, the degree of light attenuation provided by the filter 260 can be varied. Nevertheless, it is difficult and expensive to manufacture the filter 260 to attain the necessary optical density gradient.
Thus, it is desired to provide a variable optical attenuator which is inexpensive to manufacture and which can precisely control the amount of optical attenuation.
Accordingly, an object of the present invention is to provide a variable optical attenuator which has low manufacturing cost.
Another object of the present invention is to provide a variable optical attenuator which can precisely control the degree of optical attenuation.
To achieve the above objects, a variable optical attenuator of the present invention comprises a base, a cover, an attenuation device and optical fibers. The attenuation device comprises a fixed collimator, a movable collimator, a holding device and an adjusting device. The two collimators are aligned end-to-end. The holding device defines a passage in which the movable collimator is retained, and a threaded hole. The adjusting device comprises a first screw rod, a second screw rod, and a rubber ring. The first screw rod comprises a thread portion, a gear, and a round head. The thread portion of the first screw rod is rotatably engaged in the threaded hole of the holding device. The second screw rod comprises a thread portion and an adjusting slot defined in a top face of the second screw rod. The thread portion of the second screw rod meshes with the gear of the first screw rod.
When the second screw rod is rotated via the adjusting slot, the thread portion of the second screw rod drives the gear to rotate the first screw rod, and the first screw rod rotatingly drives the holding device to move toward the head or away from the head. Thus an offset, if any, between the two collimators can be adjusted. Accordingly, an amount of optical attenuation of the attenuator can be precisely controlled via the two screw rods.
Other objects, advantages and novel features of the present invention will be drawn from the following detailed description of the preferred embodiment of the present invention with attached drawings, in which: